1. Field of the Invention
This invention relates to a vibration severity indicator which provides a visual indication of the instantaneous mechanical vibration level of a vibrating object.
2. Description of the Prior Art
Numerous devices are available for determining the instantaneous vibration level of vibrating objects. See U.S. Pat. No. 3,098,379. These systems usually include a vibration detector adapted to generate an electrical signal corresponding to the instantaneous displacement, velocity or acceleration of the vibrating object and means for measuring the amplitude of the resulting electrical signal. Seismic detectors generate an electrical signal having a voltage which corresponds to the instantaneous velocity of the vibrating object. Proximity detectors and accelerometers can be employed to observe the instantaneous displacement and acceleration, respectively, of the vibrating object.
There is a need for a vibration severity indicator which can be used by relatively inexperienced operators for inspection of a variety of rotating machinery, for example, on a large ship, many different sized motors will be found which should be periodically inspected in a preventive maintenance program.
The International Standards Organization has established six different classes of machines as follows:
Class I: Individual parts of engines and machines, integrally connected with the complete machine in its normal operating condition. Production electric motors up to 15 kilowatts are typical examples of machinery in this class.
Class II: Medium-sized machines, typically electrical motors with 15-75 kilowatt output, without special foundations; rigidly mounted engines or machines, up to 300 kilowatts, on special foundations.
Class III: Large prime movers and other large machines with rotating masses mounted on rigid and heavy foundations which are relatively stiff in the direction of vibration movement.
Class IV: Large prime movers and other large machines with rotating masses mounted on foundations which are relatively soft in the direction of vibration measurement, for example, turbogenerator sets, especially those with lightweight substructures.
Class V: Machines and mechanical drive systems with unbalanceable inertia forces, due to reciprocating parts, mounted on foundations which are relatively stiff in the direction of vibration measurement.
Class VI: Machines and mechanical drive systems with unbalanceable inertia forces, due to reciprocating parts, mounted on foundations which are relatively soft in the direction of vibration measurements; machines with rotating slack coupled masses such as beater shafts in grinding mills, machines, like centrifugal machines, with varying unbalances capable of operating as self-contained units without connecting components; vibrating screens, dynamic fatigue testing machines and vibration exciters used in processing plants.
Of these six classifications, the first four classes lend themselves to vibration analysis and correction. With respect to Class I, Class II, Class III, Class IV machinery, it is possible to establish ranges of vibration severity based upon the observed vibration, measured in velocity decibels. ##EQU1## The following Table 1 shows that Class I machinery vibration may range from 0.28 to 11.2 millimeters per second RMS; for Class II machinery from 0.45 to 18 millimeters per second RMS; for Class III machinery, 0.71 to 28 millimeters per second RMS; for Class IV machinery from 1.12 to 45 millimeters per second RMS. These accepted ranges, when expressed in decibels, encompass 32 decibels. Each of the ranges can be conveniently divided into four segments, each segment having a constant decibel span of 8 decibels as shown in Table 1.
TABLE 1 ______________________________________ VIBRATION SEVERITY RANGES QUALITY JUDGEMENT VIBRATION VELOCITY Class Class Class Class mm/sec RMS Decibels I II III IV ______________________________________ 0.28 89 -- 0.45 93 A -- 0.71 97 -- A -- 1.12 101 B -- A -- 1.8 105 -- B -- A 2.8 109 C -- B -- 4.5 113 -- C -- B 7.1 117 D -- C -- 11.2 121 -- D -- C 18 125 -- D -- 28 129 -- D 45 133 -- ______________________________________